Classification of materials by elutriation



Dec. 6, L, ND S 1,890,206

CLASSIFICATION OF MATERIALS BY ELUTRIATION Filed Sept. 8, 1930 Patented Dec. 6, 1932 UNITED STATES PATENT OFFICE LEONARD ANDREWS, ,OF HOLBOB-N, LONDON, ENGLAND cnassrrrca'rron or m'rnnmns IBY ELUTR-IATION Application filed September 8, 1930, Serial No. 480,549, and in Great Britain September 19, 1929. I

admixture with liquid, for examplerwater, to the combined action of centrifugal force and.

of gravity, whereby the different solid particles of matter in the material being treated, are separated from eachother and fall at different rates in the liquid. Heretofore, a

,common way of effecting the classification of material by the method referred to, has been to deliver the mixture of solid material and liquid into a vessel, usually and hereinafter called a classifier, provided at its upper end with an overflow outlet for liquid carrying in suspension separated lighter and smaller particles of the material (herein-' after called for brevity, fine particles) and at its lower end with a valve controlled outlet for regulating the discharge of separated heavier and larger particles of material (hereinafter called for brevity, oversize particles) together with more or less liquid, the

rate of overflow of the liquid carrying the fine particles, being dependent, to a' large extent, upon the rate at which liquid withmaterial to be treated is fed into the classifier, and wherein a rotary motion is imparted to the mixture.

The present invention also has for its object to enable the proportion between the charge of separate oversize particles from the lower outle of the classifier during the working of the classifier, though a shut-off may be provided for closing such outlet, when the apparatus is not in action, and for temporarily closing the outlet at starting.

The invention also has for its object to maintain the necessary degree of fluidity of the oversize particles to ensure their proper jglischarge from the lower end of the classi- The classification of material by the elutriation method referred to, is effected, according to the present invention, by subjecting a mixture of the material and liquid to the combined action of centrifugal force and gravity within a classifier havingfree outlets at top and bottom and controlling the rate of discharge of liquid with admixed particles through the upper and lower outlets by siphonic or suction effect produced on the liquid leaving the top of the classifier. The

fluidity of the oversize'particles required for the effective discharge of such particles is maintained, when necessary, by automatic admixture of liquid therewith.

For enabling the improved method of classification to be carried out, the classifier used therefor is, according to the present invention, provided at its upper portion with a suction producing device, preferably a siphon pipe, for drawing off liquid carrying fine particles, at its lower end with a discharge 7 pipe or spigot for the free discharge, during the working of the classifier, of oversize particles and liquid, and at an intermediate part of its height with an inlet through which liquid carrying the material to be classified can be caused to enter in a tangential direction so that; a rotary motion will be imparted to such liquid and material. The upper portion of the classifier is or may be provided internally above the said inlet with annular conical passages for directing liquid carrying fine particles to the upper portion of the classifier and thence to the suction or siphon outlet, and the lower portion of the classifier 1s or may be provided with an inverted conical annular passage leading to a central discharge outlet at the bottom and w1th wh1ch are associated meanswherebyliquid, t may be clear water, can be caused to flow into 1t at a suitable point in its height and flow upward, or partly upward and partly downward, according to the amount and degree of density of oversize particles therein.

Classifiers such as described for enabling the improved method of classificatlon of ma- I the invention.

According to the construction shown, the classifier comprises a casing having a cylindrical upper portion aprovided with a central upper outlet 6 connected to a pipe. 0 adapted to act as a siphon pipe, and a lower inverted "conical portion-a connected to a central outlet pipe or spigot d, the cylindrical portionof the'casing being also provided at a lower part thereof with an inlet 0 for the material to be classified, admitted through a tangentially arranged pipe '6 The outlet pipe or spigot d is provided with a hand operated valve cl, wherebyit can be closed when the classifier is not in action and during the starting of the classifier, but is moved into a lar passage It between the two cones.

more or less open position when the classifier has been started, and'is maintained in that position to admit of a continuous discharge of oversize particles from the said pipe or spigot d. \Vithin the upper portion of the casing are preferably fixedtwo inverted hollow truncated co-axially arranged cones f and g of difi'erent internal and external diameters, the upper cone being preferably but not necessarily of greater depth than the lower cone. he upper cone is arranged to form a liquid tight joint with the upper part a of thecasing and an inwardly and downwardly extending annular passage h with the lower cone 9. The said upper cone 7 is preferably made of greater depth than the lower cone 9 and arranged to terminate near to a.

central stationary cone F, but so as to leave a narrow opening between the two cones. The upper cone fis' provided .at anlintermediate portion of its depth with annular rows of holes f for a purpose hereinafter described. The upper end of the lower cone 9 is of such a diameter as to form between itand the easing, an annular passage z'leading to the argnuuspended centrally within the lower conical portion of the casing is a vessel 7: which forms with the lower conical portion a of the caslng, an annular space m of inverted conical shape in section, communicating directly with the lower central discharge pipe or spigot (1. Means, as for instance, a central vertical pipe 0, to which the aforesaid cone' f may be' fixed, is provided for admitting liquid, for instance, clean water, to the said vessel, the lower portion of which is provided with an outlet that may conveniently be in the form of a circumferential outlet 7a, through which liquid can pass from the vessel a into the lower annular passage m. The said outlet is preferably formed between the lower edge of the vessel is and a vertically adjustable plate is so as to form an annular outlet k ofadjustable depth for the issuing liquid. (1 is a window in the lower portion a of the casing a a. i i

The operation of the classifierconstructed as hereinbefore described is as follows The material to be classified, mixed with water, is fed tangentially into the classifier, through the inlet pipe a at a reasonably high velocity so that a rotary motion or vortex action will beimparted to the entire mass of mixture within the classifier. The first effect of this vortex action is to cause the articles to impinge against the inner side of t e upper portion a of the wall of the classifier under the action of centrifugal force. The heavier particles will fall rapidly down the wall under the ,force of gravity and fall into the conical lower portion a of the classifier and be discharged with more or less of the water through the lower discharge outlet (1, while water and lighter particles will flow up the wall under the influence of the siphon action produced by the siphon pipe 0. The effect of the vortex action is to reduce a stress in the rotating mixture, causing a constant flow of mixture from the centre of the classifier to the outer periphery thereof. The upward flow of water, carrying fine particles and intermediate size particles insuspension, is directed upwardsvthrough the annular space 11' between the wall of the classifier and the lower cone 9 and-thence downwards into the .annular passage h between the two cones f and g. The greater portion of the water with the finest suspended particles therein, will pass, in the example shown, through the openings f in the cone f into the space above that cone and be carried upwards through such space, as indicated by the arrows at, at a greatly reduced velocity to the outlet 6 and siphon pipe 0, whereas the intermediate size particles will be projected downwards along the upper surface of the lower cone 9 and be thereby carried down to join the oversize particles. The downward movement of the intermediate size particles is also assisted by that portion of the stream of liquid flowing from the centre. of the classifier below the cones. vto the outer periphery thereof and thence through the annular space i and passage h, which does not pass throu h the perforations f in the upper cone f. ater will continually circulate through the annular space between the upper portion a of the casing, a, a, and the outer and lower cone g, the annular space i and the annular passage h, as indicated by the arrows 3 The relative volumes of the water-solid mixture flowing upwards or downwards under the respecing the siphon pipe 0 of such. a length and diameter, and varying its effective length, that the whole of the water tends to flow upwards through the casing a a to the upper outlet 5 thereof, or this upward flow can be reduced to any desired extent by suitably reducing the eflective length of the siphon pipe, or by admitting air into the siphon pipe by an air valve 0, thereby reducing in each case, the weight of the contents of the siphon pipe and increasing the liquid pressure at the lower spigot outlet cl, thus causing .any desired quantity of the liquid to flow through the spigot outlet, such liquid carrying the oversize particles with it.

In the example now being described, the

lower open end of the siphon ipe c, which is at a lower level than the spigot outlet (1, is provided with holes 0 and terminates a plate 0 to which is attached a discharge pipe 8 provided with a valve t. Carried by the plate 7' and surrounding the lower end portion of the siphon pipe 0, is a cylindrical casing u that forms, with the said lower portion of the siphon pipe 0, a chamber a provided at its upper portion with an overflow outlet connected by a pipe '0 to the discharge pipe 8 below the valve't. The arrangement is such that by opening or closing the valve 27 to varying extents, water can be caused to enter the chamber u through the holes 0 and be caused to rise therein to varying levels, which may be indicated by a gauge glass w, so as to admit of the effective length of the siphon pipe being varied to suit requirement.

It is well known that the velocity of flow of sand and water through an outlet of given area under a given pressure, depends upon the thickness of the film of watertseparating the particles of sand, or in other words, upon the fluidity of the mixture.

If particles of sand are allowed to settle into practically intimate contact with each other, the velocity is greatly reduced, and subsequently the weight of solid matter discharged in unit time is also much lower. The rate of discharge from a classifier provided at its lower end with an open spigot, is thus liable to be inversely proportional to the depth of the sand level above the spigot outlet. The result is, the greater the quantity of sand in the classifier, the slower will be its discharge, which, obviously, is the reverse of the condition required for practical working. The original control of the discharge of liquid from the classifier can however according to the present invention, be adjusted so that the quantity of liquid discharging from the spigot outlet (2 is at all times in excess of that necessary to maintain fluidity of the mixture of liquid and oversize particles, in which case a high rate of discharge will be maintained, and no seal will be formed by the said particles. Under such conditions, the rate of discharge of liquid and oversize particles will tend to increase with an increasing quantity particles suspended in the liquid to. be carried down with the o .rersize particles, which may be a detrimental condition where a discharge of oversize particles only is required.

- The aforesaid vessel is is provided to main: tain the fluidity of the mixture of liquid and oversize particles, and consequently a rate of discharge increasing with the depth of the oversize particles, without allowing fine particles to be discharged with such oversize particles.

This result is obtained as follows Adjustment of the siphonic action of the pipe 0 is made so that the rate of discharge of liquid and oversize particles through the spigot outlet 03 is slightly less than the rate at which oversize particles are fed into the classifier, with the result that a gradually increasing depth of oversize particles is formed in the lower annular passage m of the classifier. It is obvious that the whole of the clear water admitted to the aforesaid vessel is will flow freely through the circumferential outlet in in the vessel. Owing; to the fact that there is a gradual decrease of pressure below atmospheric pressure from the bottom to the top of the classifier, due to the siphon action described, the whole, or practically the whole, of the clear water issuing from the vessel is, acting as teetering water, will flow upwards and this will continue until the oversize particles have accumulated to such a depth above the outlet is, as appreciably to resist the upward flow, when a portion of the issuingteetering water will be directed downwards, thus increasing the fluidity of the oversize particles flowing towards and through the spigot outlet (1 and thereby increasing the rate of discharge of the said particles and tending to lower or reduce the depth of the bed of oversize particles in the lower part of the elastifier. By the means described, it is found by experiment that the bed of oversize particles maintains a practically constant level independent of the rate at which the oversize particles is fed into the classifier. A portion of the water issuing from the vessel 70 flows upwards the whole time maintaining a loof'e formation throughout the entire bed of oversize particles and also checking the descent of fine particles with the oversize particles.

The necessary velocity required to maintain the vortex action of the mixture of liquid and material within casing a, a of the classifier can be produced by means of a pump 1, for instance a centrifugal pump, drawing its supply from a feed hopper 2. Or, alternately, the mixture of liquid and material may be supplied under a head suflicient to impart, by mere gravity, the necessary velocity to the mixture entering. the classifier.

What I claim is'-:-. 1. For the classification of material by elutriation, a classifier comprising a casing. having upper and lower outlets, suction means" connected to the upper outlet of said casing and adapted to draw ofl liquid carrying fine' 2. A classifier according to claim 1, where-V in the said cones are inverted cones arranged concentrically one above the other and spaced apart to 'form between them a downwardly and inwardly inclined annular passage open at its lower end and in communication through the upper portion of said casing with the upper outlet thereof, the outer periphery of the lower cone being arranged to form an annular outlet passage between it and the adjacentportion of said casing, and the upper cone being connected at its outer periphery to said casing. v 3. A classifier according" to claim 1, wherein the said cones are inverted cones arranged concentrically one above the other and spaced apart to form between them a'downwardly and inwardly inclined annular passage open at its lower end and in communication;

through the upper portion of said casing, with the'upper outlet thereof, the outer periphery of the lower cone being arrangedto form an annular outlet passage between its outer periphery and the adjacent portion of said casing and the upper'cone being connected at its outer periphery to said casing and provided with outlet apertures between its upper and lower ends.

4. For the classification of material by elutriation, a classifier comprisinga casing having free outlets at its upper and lower end and between such outlets a tangentially arranged inlet for mixed liquid and materials to be classified,a'siphon pipe connected to the upper outlet, means for varying the weight of the column of mixed liquid and fine particles in said siphon pipe and means located with'- in said casing between said upper outlet and said inlet adapted to separate intermediate size particles from liquid flowing to said outlet and permit them to fall into the lower part of said casing.

5.,For the classification of materials ,by elutriation, a classifiercomprising a casing having an upper cylindrical portion and a at the top and with a lateral inlet intermediate its u per and lower ends and said lower portion eing provided with an outlet at the bottom, an external siphon pipe connected to the upper outlet, means for varyin the weight of the column of mixed liquid an fine particles flowing, through said siphon pipe, a pipe adapted to discharge a mixture of liquid and material to be classified, in a tangential direction through said inlet, a discharge pipe connected to the lower end of the portion of said casing and adapted to admit of free and continuous discharge of liquid and separated oversize particles therethrdugh, a valve whereby said discharge pipe can be closed when'said classifier is not in use, a water vessel arranged centrally within the lower portion of the lower inverted conical portion of the classifier casing and having a circumferential outlet adapted to discharge water into a bed of oversize particles formed around said vessel and a pipe adapted to supply water to-said water vessel.

6. Apparatus according to claim 5 wherein there are arranged in the upper portion of the classifier casing and above the inlet for mixed liquid and solid material two superposed inverted truncated coves and a central cone, the two superposed cones being arranged to form between them an annular downwardly and inwardly inclined passage open at top and bottom, the lower cone being 7 7. For the classification of material by elutriation, a classifier comprising a casing having an upper portion with a central free outlet at the top and a lower inverted conical ortion having a central free outlet at the ottom, an external downwardly extending siphon pipe connected to the upper outlet of said casing and adapted to draw ofi liquid carrying fine particles of separated material, means for varying the weight of the column of the mixture in said siphon pipe, a discharge-pipe connected to the lower outlet of said casing and adapted to admit of the free and continuous discharge of separated oversize particles of material and liquid, means adapted to discharge into said casing between its upperand lower outlets, and in a tangen- 'tial direction, a mixture of liquid and material, to be classified, and means for introducmg liquid into the lower portion of said classifier, sald means comprising a vessel arranged centrally within the 'lower'portion of the classifier and adapted to admit of liquid issuing circumferentially therefrom and mixing with the surrounding bed of oversize particles and mans for supplying liquid to said vessel. Signed at London, England this 29th day of August, 1930.

LEONARD ANDREWS, 

